1. Field
The present disclosure is directed to a method and apparatus for determining lens shading correction for a multiple camera device with various fields of view.
2. Introduction
Presently, portable devices, such as mobile phones, tablet devices, digital cameras, multimedia devices, and other types of computing and electronic devices often include a digital camera device that is utilized to capture digital images. A digital camera includes a lens and an image sensor. One issue that arises in the operation of image sensors is the need to perform lens shading correction. An image sensor typically has a two-dimensional array of photo-sensitive pixels. The camera lens can be a single lens or a micro-lens array that focuses light onto individual pixels of the image sensor. However, various imperfections in the camera lens create a shading effect. One common shading effect is that that the image is brighter in the center and decreases in brightness at the edges of the pixel array. More generally there will be a two-dimensional variation in shading across the array of pixels caused by the optical elements in the optical assembly and the difficulties in uniformly projecting an image across the field of view of the image sensor. Uncorrected shading effects can result in undesirable variations in intensity across an image that may be discernable to an end user. Lens shading correction algorithms are used to correct for shading in an image sensor. Empirical data is used to determine coefficients of a gain correction function that is used to adjust the gain of individual pixels to compensate for the lens shading.
Some portable devices include multiple digital cameras that face in the same direction. Specifically, every camera in a multiple camera system has a different field of view of the scene from each other. The multiple digital cameras in such a system can generate multiple images with different fields of view of the same scene and the multiple images can be merged into one image. Unfortunately, without a matching algorithm, different lens shading corrections applied to different cameras in a multiple camera device cause imperfections when images from multiple cameras are combined. Thus, there is a need for a method and apparatus for determining lens shading correction for a multiple camera device with various fields of view.